Method and apparatus for measuring channel quality using a smart antenna in a wireless transmit/receive unit

ABSTRACT

A method and apparatus for measuring a channel quality in wireless transmit/receive units (WTRUs) which are equipped with a subscriber based smart antenna. The WTRUs are equipped with a smart antenna so that the WTRU generates a plurality of directional beams and, optionally, an omni-directional beam. A dwell time is provided in a measurement period to switch a beam from an active beam to a non-active beam. The active beam is one of the plurality of directional beams or, optionally, the omni-directional beam, for communication with one or more serving base station(s). A beam is switched to a non-active beam at the initiation of the dwell time. Signals are received through the switched non-active beam, and samples of the received signals are generated. The samples are stored in a memory. Channel quality is measured using the samples, whereby the dwell time to measure the channel quality is minimized.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/543,012 filed Feb. 6, 2004, which is incorporated by reference as iffully set forth.

FIELD OF INVENTION

The present invention is related to wireless transmit/receive units(WTRUs). More particularly, the present invention is related to a methodand apparatus for measuring channel quality in WTRUs which are equippedwith a subscriber based smart antenna.

BACKGROUND

One of the important issues in wireless communication systems iscapacity of the system. Smart antenna technology has been developed toincrease wireless communication system capacity. Smart antennas arecurrently used in base stations, access points, and WTRUs. One form ofsmart antenna technology is the use of multiple radiating elements inone or more antennas to generate a plurality of directional beams. Withthis form of smart antenna, use of the directional beam or beams withthe best quality reduces the amount of transmit power needed, usuallyresulting in increased system capacity.

In mobile communication systems, WTRUs typically monitor quality, suchas signal-to-interference ratio (SIR), of the cell(s) currently servingthe WTRU as well as neighboring cells. In WTRUs employing smart antennatechniques which generate a plurality of beams, the WTRUs would need tomonitor the quality of the plurality of beams for all of these cells (ora subset of these cells).

Hereafter, the terminology “active beam” refers to a beam that a WTRUuses for its data transmission and reception, and the terminology“serving base station” refers to a base station currently communicatingwith the WTRU. The terminology “current beam” refers to the beamcurrently being formed by the element(s) of the antenna(s). In order tomeasure quality (such as SIR) on channels that correspond to non-activebeams, the WTRU must switch its current beam to the non-active beam andobserve the channel for some time. This time period is referred to as“dwell time”, T_DWELL. Once the dwell time expires, the WTRU switchesthe current beam back to the original active beam for normalcommunication with the serving base station(s).

In the prior art, in order to measure the signal quality on inactivebeams on multiple base stations, the WTRU switches its current beam tothe inactive beams for each of those base stations for a period of time.For example, if a WTRU uses a smart antenna which is configured togenerate three beams (a left beam, an omni-directional beam and a rightbeam), and if the right beam is an active beam and the WTRU has tomeasure SIRs to three base stations (BS-1, BS-2, and BS-3) using theleft beam, the WTRU first switches the current beam from the right beamto the left beam for T_DWELL to measure the SIR to BS-1. During thistime, for a CDMA system for example, the WTRU despreads the receivedsignal using the known pilot (or other) signal transmitted from BS-1,and the despread values are used to estimate the SIR to BS-1. In orderto measure the SIR to BS-2, the WTRU again switches the current beam tothe left beam for another T_DWELL, and receives signals and despreadsthe received signal using the known pilot (or other) signal transmittedfrom BS-2. The despread values are then used to estimate the SIR toBS-2. Similarly, in order to measure the SIR to BS-3, the WTRU has toswitch the current beam to the left beam again for another dwell time.Therefore, in this example, the WTRU must stay on the left beam for3*T_DWELL to measure the SIRs on the left beam for all three basestations.

Data reception is degraded during the dwell time since the WTRU operatesbased on the assumption that the channel it sees corresponds to theactive beam. In the foregoing example, data reception is interrupted for3*T_DWELL. More generally, in accordance with the prior art, a WTRU mustswitch a beam for N*T_DWELL, to measure the SIR to N base stations on aninactive beam. Since data can be continuously transmitted to the WTRU,it is necessary to keep the dwell time as short as possible.

It is noted that the operations for despreading above (or other meansfor correlating the received signal with a known transmit signal) aredone in real-time using the correlation resources in the mobile receiver(hardware blocks and/or software blocks in a microprocessor or DSP).

SUMMARY

The present invention is a method and apparatus for measuring a channelquality in WTRUs which are equipped with a subscriber based smartantenna. The WTRUs are equipped with a smart antenna so that the WTRUgenerates a plurality of directional beams, and, optionally, anomni-directional beam. A dwell time is provided in a measurement periodto switch the current beam from an active beam to a non-active beam. Theactive beam is one of the plurality of directional beams or, optionally,the omni-directional beam, for communication with one or more servingbase station(s). The current beam is switched to a non-active beam atthe initiation of the dwell time. Signals are received through thenon-active beam, and samples of the received signals are generated. Thesamples are stored in a memory. The current beam may be switched back tothe active beam or another non-active beam. Channel quality is measuredusing the stored samples, whereby the dwell time to measure the channelquality is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a wireless communication system in accordancewith the present invention.

FIG. 2 is a flow diagram of a process for measuring a channel qualityusing a smart antenna in a WTRU in accordance with the presentinvention.

FIG. 3 is a flow diagram of a process for measuring a channel qualityusing a smart antenna in a WTRU in accordance with another embodiment ofthe present invention.

FIG. 4 shows a timing relationship between a dwell time and ameasurement period in accordance with the present invention.

FIG. 5 is a block diagram of a WTRU in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “WTRU” includes but is not limited to a userequipment, a mobile station, a fixed or mobile subscriber unit, a pager,a wireless local area network (WLAN) client station, or any other typeof device capable of operating in a wireless environment. When referredto hereafter, the terminology “base station” includes but is not limitedto a Node B, a site controller, an access point, or any other type ofinterfacing device in a wireless environment.

FIG. 1 is a diagram of a wireless communication system 100 in accordancewith the present invention. The wireless communication system 100comprises a plurality of base stations 104 a, 104 b and WTRUs 102. Aregion in the wireless communication system 100 is divided into aplurality of cells and each cell is served by each base station 104 a,104 b. A WTRU 102 is equipped with a smart antenna and generates aplurality of directional beams to communicate with a base station 104 a,104 b. In FIG. 1, it is depicted that a WTRU generates three directionalbeams. However, it should be understood that the WTRU may generate anynumber of directional beams and may also generate and use anomni-directional beam.

The WTRU 102 receives signals from a serving base station (such as basestation 104 a) and from a plurality of non-serving base stations (suchas base station 104 b), and continually monitors channel quality to thebase stations 104 a, 104 b. It should be noted that FIG. 1 illustratesonly one serving base station as an example, not as a limitation andthat there may be more than one serving base station, whereby the WTRU102 may select or combine signals from the serving base stations (forexample, perform soft combining of the signals from the active set basestations in a CDMA system). The channel quality is evaluated in terms ofSIR or other relevant parameters.

In measuring channel quality to the base stations 104 a, 104 b withnon-active beams, the WTRU 102 switches the current beam between anactive beam 106 a and non-active beams 106 b. In FIG. 1, the WTRU iscurrently communicating with a serving base station BS-0 104 a using anactive beam 106 a. The WTRU 102 periodically switches the current beamto non-active beams 106 b and measures a channel quality to basestations BS-0, BS-1, BS-2 and BS-3, respectively. The WTRU does not haveto use all non-active beams 106 b, but may choose only a portion of thenon-active beams 106 b.

FIG. 2 is a flow diagram of a process 200 for measuring channel qualityusing a smart antenna in a WTRU 102 in accordance with the presentinvention. The process is typically initiated by a measurementtriggering signal or event. After the process 200 is initiated, it isdetermined whether it is time to start a dwell period (step 202). Thedecision whether it is time to start a dwell period may be hardwareand/or software controlled. One example is making the decision based onthe expiration of a timer that is initiated at the start of themeasurement period and expires after a pre-programmed wait period (whichcould be zero, a fixed value, or a variable value such as a fixed valuewith random jitter).

The measurement triggering signal is an external event that marks thebeginning of a measurement period and starts the procedure 200. Ameasurement triggering signal may be any hardware or software event toindicate the start of a measurement period (for example: the change ofvoltage on a pin of an integrated circuit, the expiration of a timer, ora software process call to the process 200). The measurement triggeringsignal/event marks the beginning of a measurement period. Themeasurement triggering signal/event can occur periodically or notperiodically, resulting in a measurement period that is fixed orvariable. The simplest example is the periodic case; in this case a newmeasurement period is triggered immediately after a previous measurementperiod ends.

If it is not time to start a dwell period (step 202), then the process200 waits at step 202 until it is time to start the dwell period. If itis time to start the dwell period, a dwell time is provided during themeasurement period to measure a beam (step 204). Then, a non-active beamthat has not yet been measured in the current measurement period ischosen for measurement (step 206) and the current beam is switched tothat non-active beam (step 208).

FIG. 4 shows a timing relationship between a dwell time and ameasurement period in accordance with the present invention. More thanone dwell time may be provided in one measurement period depending onprocessing capacity, which will be explained in detail hereinafter. Thedwell time may start not only at the beginning of the measurementperiod, but may start from any place in the measurement period inaccordance with the hardware and/or software that controls this decision(e.g., software parameters). The length of the dwell time is set toprovide a sufficient time period for a WTRU 102 to collect enoughsamples to measure the channel quality of base stations with the desiredaccuracy. The place of the dwell time in a measurement period and theduration of the dwell time may be fixed or variable. Therefore, adifferent number, different duration, and different place of dwelltime(s) may be provided in each measurement period.

After the current beam is switched to the non-active beam (step 208),the WTRU 102 receives signals from serving and non-serving base stations104 a, 104 b through the switched non-active beam 106 b (step 210). TheWTRU 102 may select particular serving and non-serving base stationsbased on predetermined criteria, instead of processing all signals fromserving and non-serving base stations 104 a, 104 b. The received signalsare sampled (step 212) and the samples are stored in a memory (step214). Once the samples are generated, the WTRU 102 computes the channelquality for the serving base station(s) 104 a and non-serving basestations 104 b (step 216). The WTRU 102 may start to compute the channelquality simultaneously while samples are generated and stored.Alternatively, the WTRU 102 may start to compute the channel qualityafter all the samples are generated and stored. The samples do not haveto be processed before the current beam is switched to another beam, butmay be processed in parallel with other procedures (for example, whennew samples are generated with another beam) when the processing powerof the WTRU 102 is sufficient for these multiple parallel processes.

After samples are generated and stored, it is determined if there isanother non-active beam 106 b to be measured (step 218). All non-activebeams 106 b do not have to be measured; the beams to be measured can bea select set of non-active beams. If there are no more non-active beamsto be measured, the current beam is switched back to the original activebeam 106 a (step 220) and the process terminates (step 222) until thenext measurement trigger.

If it is determined that there is another non-active beam 106 b to bemeasured (step 218), a decision is made whether to spread out the dwelltimes (step 224). Spreading out the dwell times allows a gap betweenmeasurements on non-active beams. Whether a gap is desired could be apre-determined configuration decision or be based on external factors,such as signal quality. If a gap is desired, the process 200 switchesback to the active beam (step 226) and then waits for the start of thenext dwell period (step 202). If a gap is not desired (step 224), theprocess 200 gets the dwell time (step 204).

FIG. 3 is a flow diagram of a process 300 in accordance with anotherembodiment of the present invention. The process is typically initiatedby a measurement triggering signal or event. After the process 300 isinitiated, it is determined whether it is time to start a dwell period(step 302). The decision whether is it time to start a dwell period maybe hardware and/or software controlled. If it is not time to start adwell period, then the process 300 waits at step 302 until it is time tostart the dwell period. If it is time to start the dwell period, a dwelltime is provided during the measurement period to measure a beam (step304). Then, a non-active beam is chosen for measurement (step 306) andthe current beam is switched to that non-active beam (step 308). Thenon-active beam chosen is one that has not yet been measured in thecurrent measurement period or one for which measurements have not beencompleted for all desired base stations in the current measurementperiod.

After the current beam is switched to the non-active beam (step 308),the WTRU 102 receives signals from serving and non-serving base stations104 a, 104 b through the switched non-active beam 106 b (step 310). TheWTRU 102 may select particular serving and non-serving base stationsbased on predetermined criteria, instead of processing all signals fromserving and non-serving base stations 104 a, 104 b. The received signalsare sampled (step 312) and the samples are stored in a memory (step314).

At the same time, the generated samples may be processed simultaneouslyto generate channel quality estimates for one or more base stationswhile samples are generated and stored (step 316). The number of basestations for which channel quality estimates can be computed while thesamples are being stored is dependent on the processing power available.

It is then determined whether enough resources are available, withoutproviding another dwell period in the current measurement period, toprocess the channel quality estimates for the current non-active beamfor all the remaining base stations (for which these estimates areneeded) that were not processed in step 316 (step 318). Thedetermination is made based on the amount of resources available forestimating channel quality (for example, correlation resources inCDMA2000), which drives how much processing can be done in parallel, andthe number of non-active beams and the number of base stations for whichchannel quality estimates are needed in the measurement period. The goalis to maximize parallelism so the current beam can return to, and remainon, the active beam as much as possible to minimize performancedegradation.

If the resources are not sufficient, additional dwell time is needed anda decision is made whether to spread out the dwell times (step 320).Additional samples for the non-active beam may be collected during anadded dwell time, which may be provided consecutively to the currentdwell time or spread out during the same measurement period. Spreadingout the dwell times allows a gap between measurements on non-activebeams in which signals are received on the active beam. Whether a gap isdesired could be a pre-determined configuration decision or be based onexternal factors, such as signal quality. If a gap is desired, theprocess 300 switches back to the active beam (step 322) and then waitsfor the start of the next dwell period (step 302). If a gap is notdesired (step 320), the process 300 gets the dwell time (step 304).

As an alternative (not shown) to steps 320-322, the current beam is kepton the non-active beam and another dwell time is provided. During thisadded dwell time, the stored samples are processed to obtain the channelquality for additional base stations for the current non-active beam.After the dwell time, the process 300 returns to step 318 to again checkif resources are sufficient for processing any remaining base stationswithout adding another dwell time.

If there are sufficient resources to process the remaining base stations(step 318), it is determined if there is another non-active beam 106 bto be measured (step 324). All non-active beams 106 b do not have to bemeasured; the beams to be measured can be a select set of non-activebeams. If there are no more non-active beams to be measured, the currentbeam is switched back to the original active beam 106 a (step 326), thesamples for the remaining base stations are processed (step 328), andthe process terminates (step 330) until the next measurement trigger.

If it is determined that there is another non-active beam 106 b to bemeasured (step 324), then two steps occur in parallel. The first step isto continue to process the samples for the remaining base stations onthe currently selected beam (step 332). Second, a decision is madewhether to spread out the dwell times (step 320). If a gap is desired,the process 300 switches back to the active beam (step 322) and thenwaits for the start of the next dwell period (step 302). If a gap is notdesired (step 320), the process 300 gets the dwell time (step 304).

In step 332, the samples do not have to be processed before the currentbeam is switched to another beam (active or inactive), but may beprocessed in parallel with other procedures (for example, when newsamples are generated with another beam) when the processing power ofthe WTRU 102 is sufficient for these multiple parallel processes.

If a WTRU has processing capability to perform channel qualityestimation to M base stations in a single dwell time, and there are atotal of N base stations for which the WTRU has to measure channelquality, then to avoid adding additional dwell times for a givennon-active beam, the WTRU has to perform channel quality estimation toK=N−M base stations while the beam is switched back to the active beam106 a or to other non-active beams 106 b. In order to estimate channelquality for K base stations, there is a trade-off between additionalprocessing power and additional dwell time. Additional processingcapability may be provided (i.e., add hardware and/or microprocessor/DSPcapability or the like) or additional dwell time may be provided toswitch the current beam to non-active beams 106 b for additional periodsin which channel quality measurements can be made. At one extreme,additional processing capability could be added such that the channelquality of all base stations could be estimated in a single dwell time.At the other extreme, additional dwell times could be added with noadditional processing capability of the WTRU 102. The dwell time may beadded consecutively or may be spread out over the single measurementperiod.

FIG. 5 is a block diagram of a WTRU 102 in accordance with the presentinvention. The WTRU 102 comprises a smart antenna 502, a beam switchingunit 504, a sampler 506, a memory 508, a measurement unit 510, and acontroller 512. The smart antenna 502 is configured to generate aplurality of directional beams, and, optionally, an omni-directionalbeam. Each beam is used to receive signals transmitted by base stations.The beam switching unit 504 is for switching the current beam to one ofthe plurality of directional beams and between one of the directionalbeams and the omni-directional beam (if an omni-directional beamexists). The sampler 506 receives the signals from the smart antenna 502which is directed toward a particular direction and generates samples ofthe received signals. The samples are stored in the memory 508. Themeasurement unit 510 performs a physical measurement (also called anestimation) of a channel quality using the samples. The controller 512controls the beam switching unit 504 such that the current beam isswitched to a non-active beam at the start of a dwell time and switchesback to the active beam for communication with a serving base station atthe expiration of the dwell time or multiple dwell times, as needed. Thedwell time is minimized by performing the physical measurements whilethe samples are being collected and stored and while the current beam isswitched back to the active beam or another non-active beam.

Using terminology from FDD and CDMA2000, the base stations that the WTRUhas to measure SIR estimates for include the base stations in thecandidate set and/or the base stations in the neighbor set and/or thebase stations in the active set.

The method of the invention is not limited to a two-dimensional beamswitching, but also applicable to three-dimensional beam switching.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

1. A method for measuring channel quality in a wireless transmit/receiveunit (WTRU), the WTRU being equipped with a smart antenna for generatinga plurality of beams, selected from the group consisting of directionalbeams and an omni-directional beam, the method comprising the steps of:(a) providing a dwell time in a measurement period to switch a beam froman active beam to a non-active beam, the active beam being a beam forcommunication with a serving base station; (b) switching a beam to anon-active beam at the initiation of the dwell time; (c) receivingsignals from the serving base station and a non-serving base stationthrough the switched non-active beam at the same time; (d) generatingsamples of the received signals; (e) storing the samples in a memory;(f) measuring a channel quality to the serving base station and achannel quality to the non-serving base station, respectively, using thestored samples; and (g) switching the beam back to the active beam. 2.The method of claim 1, wherein the WTRU simultaneously measures at leastone of the channel quality to the serving base station and the channelquality to the non-serving base station during the dwell time whilegenerating the samples.
 3. The method of claim 1, further comprising thestep of determining whether resources in the WTRU are sufficient tomeasure a channel quality for all the serving and non-serving basestations in a current measurement period, wherein the beam is switchedback to the active beam if the resources are sufficient, and additionaldwell time is provided to perform further measurements before switchingthe beam to the active beam if the resources are not sufficient.
 4. Themethod of claim 3, wherein the additional dwell time is provided notconsecutively to the current dwell time.
 5. The method of claim 3,wherein the additional dwell time is provided consecutively to thecurrent dwell time.
 6. The method of claim 1, wherein the WTRU isconfigured to generate more than two beams, whereby steps (a)-(f) arerepeated for all the remaining non-active beams, respectively.
 7. Themethod of claim 6, wherein the beam is switched from the non-active beamto the active beam before switching to another non-active beam.
 8. Themethod of claim 7, wherein a gap is provided before the beam is switchedto another non-active beam.
 9. The method of claim 6, wherein the beamis directly switched from the non-active beam to another non-active beambefore switching back to the active beam.
 10. The method of claim 9,further comprising the step of determining whether resources in the WTRUare sufficient to measure a channel quality for all the serving andnon-serving base stations in a current measurement period, wherein thebeam is switched to a different non-active beam if the resources aresufficient, and additional dwell time is provided to perform furthermeasurements if the resources are not sufficient.
 11. The method ofclaim 1, wherein the channel quality is measured by asignal-to-interference ratio (SIR).
 12. The method of claim 11, whereinthe SIR is measured using known code sequences with which correlationcan be performed.
 13. The method of claim 1, wherein the measurementperiod is provided periodically.
 14. The method of claim 1, wherein themeasurement period is not provided periodically.
 15. A wirelesstransmit/receive unit (WTRU), comprising: a smart antenna configured togenerate a plurality of beams, selected from the group consisting ofdirectional beams and an omni-directional beam, an active beam being abeam for communication with a serving base station; a beam switchingunit for switching beams; a sampler for generating samples of receivedsignals received from the serving base station and a non-serving basestation at the same time via one of the beams; a memory for storing thesamples; a measurement unit for performing measurements of a channelquality to the serving base station and channel quality to thenon-serving base station, respectively, using the stored samples; and acontroller for switching a beam from an active beam to a non-active beamduring a dwell time which is provided at least once in a measurementperiod and switching the beam back to the active beam, wherein the WTRUperforms physical measurements of channel quality to the serving basestation and channel quality to the non-serving base station using thestored samples such that the dwell time to measure the channel qualityis minimized.
 16. The WTRU of claim 15, wherein the measurement unitmeasures at least one of the channel quality to the serving base stationand the channel quality to the non-serving base station using thesamples when the beam is switched to the non-active beam.
 17. The WTRUof claim 15, wherein the controller determines whether resources in theWTRU are sufficient to measure a channel quality for all the serving andnon-serving base stations, wherein the controller switches the beam tothe active beam if the resources are sufficient, and the controllerprovides additional dwell time to perform further measurements beforeswitching back to the active beam if the resources are not sufficient.18. The WTRU of claim 17, wherein the additional dwell time is providednot consecutive to the current dwell time.
 19. The WTRU of claim 17,wherein the additional dwell time is provided consecutively to thecurrent dwell time.
 20. The WTRU of claim 15, wherein the smart antennais configured to generate more than two beams and the controllerperforms a measurement of channel quality using at least one non-activebeam.
 21. The WTRU of claim 20, wherein the beam is switched from thenon-active beam to the active beam before switching to anothernon-active beam.
 22. The WTRU of claim 21, wherein a gap is providedbefore the beam is switched to another non-active beam.
 23. The WTRU ofclaim 20, wherein the beam is directly switched from the non-active beamto another non-active beam before switching back to the active beam. 24.The WTRU of claim 23, wherein the controller determines whetherresources in the WTRU are sufficient to measure a channel quality forall the serving and non-serving base stations, wherein the controllerswitches the beam to a different non-active beam if the resources aresufficient, and the controller provides additional dwell time to performfurther measurements if the resources are not sufficient.
 25. The WTRUof claim 15, wherein the channel quality is measured by asignal-to-interference ratio (SIR).
 26. The WTRU of claim 25, whereinthe SIR is measured using known code sequences with which correlationcan be performed.
 27. The WTRU of claim 15, wherein the measurementperiod is provided periodically.
 28. The WTRU of claim 15, wherein themeasurement period is not provided periodically.